1. Field of the Invention
Aspects of the present invention relate to an electrophotographic image forming apparatus, more particularly, to an image forming apparatus where the structure of the driving unit in a transferring unit is improved.
2. Description of the Related Art
An electrophotographic image forming apparatus is an apparatus for forming an image on a printing medium through a series of processes that include charging with electricity, exposing, developing, transferring and cleaning. The electrophotographic image forming apparatus includes a photosensitive body, an exposing unit (not shown) that exposes the photosensitive body according to image information, a developing unit (not shown) that develops the photosensitive body with a toner and forms a toner image on a surface of the photosensitive body, and a transferring unit.
In a multi-pass image forming apparatus that has a single photosensitive body and a single exposing unit in particular, the transferring unit includes a transferring belt, a middle transferring roller that transfers a toner image on the photosensitive body to the transferring belt, and a transferring roller that transfers the toner image on the transferring belt to a printing medium.
The multi-pass image forming apparatus develops the photosensitive body four times with different colors of toners such as yellow (Yel), magenta (Mag), cyan (Cyn) and black (Blk), respectively, thereby forming a color image. Then, the different colors of toners developed on a surface of the photosensitive body are transferred to the transferring belt by the middle transferring roller.
Accordingly, if the transferring belt circulates around a track four times, toner images of YelMagCynBlk colors on surface of the photosensitive body are sequentially and overlappingly transferred to the surface of the transferring belt, thereby forming a color toner image on the transferring belt. The color toner image is transferred by the transferring roller to the printing medium that passes through the transferring belt and the transferring roller.
Here, the transferring roller is spaced away from the transferring belt until the transferring belt circulates four times to completely form the color toner image thereon. Then, the transferring roller approaches the transferring roller to transfer the color toner image on the printing medium after completion of the color toner image on the transferring belt.
Thus, the transferring unit of the multi-pass type further includes a transferring roller driver that approaches the transferring roller to the transferring belt or spaces the transferring roller away from the transferring belt. The transferring roller driver is disclosed in Transfer Device of Color Laser Printer, KR Patent Application No. 2002-43012 (Transferring Apparatus of Color Laser Printer, Choi, U.S. Pat. No. 6,862,421) (hereinafter, referred to as “prior art”).
The prior art regulates the position of the transferring roller, thereby forming a uniform transferring nip between the transferring belt and the transferring roller. On the other hand, the prior art has a complicated structure for bringing the transferring roller toward and spacing the transferring roller away from the transferring belt. In the prior art, parts are manufactured separately and then combined, in particular, a member applied with an elastic force so that the transferring roller approaches the transferring belt and a lever applied with a spacing external force so that the transferring roller is spaced away from the transferring roller by a. This separate manufacture followed by mechanical combination decreases productivity and increases cost.